Grate the sweet potatoes with the shredding disk of a food processor (recommended), or on the large-hole side of a box grater.
Heat the oil in a wok or large skillet (cast iron works best) over medium-high, until the oil shimmers.
Add the sweet potato grates and cooking, stirring frequently until the edges begin turning golden brown. Mix in the scallions.
Pour in the egg and stir constantly until the curds have mixed thoroughly into the potatoes.
Drizzle stir fry sauce over the potatoes (a scant tablespoon) and mix well.
Add the vegetables and cook until slightly softened but vividly colored.
Taste, and add more stir fry sauce as desired (I like another tablespoon or two -- everything thinly coated in sauce, but not dripping).